maybe a pick (looks like a dentist pick, the seals resist pretty good and I can never seem to get pliers in there), a 14mm socket (for the magnet nut), a phillips (+) or flathead (-) screwdriver (depends what screws your coil uses, most can use either head) and a tiny bottle of superglue (you only need a drop). And whatever screwdriver to take off the magneto cover, obviously. And a hammer, maybe.
#1. Take off the cover
#2. Use your 14mm socket to remove the nut on top of the magnet (if you have a marker laying around, mark the top side of your magnet, they keyhole is off-center and putting it on with the magnet upside down will change your timing, potentially enough to prevent starting). You may need to jam something between the coil mount and the magnet to stop it from spinning while you unscrew this nut.
#3. Remove magnet
#4. Remove magneto coil (watch the wires! they're not very strong and can break easily, support it somehow or remove it completely for now).
#5. the plate under the magnet just pops off, it may be stuck the first time from the pressure of the screws just pry it off.
#6 pick that seal out, I used a hunting knife the last time (I didn't have a pick), but anything to get in there and pop it out will work.
#7 Replace seal with a new one, if you have any sealants like Seal-all, you can use it around the edge of the seal for some extra false-hope.
#8 Replace metal plate
#9 replace magnet coil
#10 Replace half-moon key on magnet shaft (use a dab of superglue, this is [in my experience] the most frustrating key to keep in place)
#11 replace magnet, marked side out, you may need to hammer it down, it should sit nearly flush with the coil mount, perhaps slightly lower. Make sure to match the half-moon key hole position, it'll be a really tight fight, thats why you use superglue
#12 replace nut
#13 test, and pray.